jfg455

Hello. new to the board but an old hat with 3rd gens and GM's in general. I am looking for input on an injector manufacturer and to double check my math for size requirements. I am building a 383 for my 89 formula (8.2:1 twisted wedge heads, forged internals, TPI or mini ram, T76 Q .96ar ) and I think that I need 83lbs injectors for it. I estimated it at 900 crank HP and used a bunch of injector calculators to come up with this number. Also who makes a good 83 lbs injector? I am using methanal injection after 5 psi (LOOKING TO RUN 22 - 24 LBS MAX). I guess I have a third question can I run this setup with a 749 ecu or do I have to step up to a big stuff 3? Thanks for your help. John

junkcltr

iTrader: (1)

Siemens Deka. www.racetronix.com

For 900 HP you will be over 15 PSI with the 76mm unit. Stock 749 ECM will do it with a patch to up it from 2 bar to 3 bar. You need a 3 bar sensor also. Aftermarket ECM will do it also.......get out the checkbook for that.

rob_m

If you're talkin' gasoline, then even 72's will do it. 72's at 90% duty cycle and .55 BSFC is about 940 FWHP. 83's will be plenty. At the kind of boost you're planning I'd think about an intercooler even w/ the methanol injection.......

junkcltr

iTrader: (1)

Yes, the 72's would do it. They would be easier to tune at idle and low throttle settings. When you have injectors that big, the stock TPI ECMs are almost, if not completely un-usable because of the double fire batch mode. You can try the single fire mode with them but the engine will idle with more lope.

Using an alternate bank fire ECM (megasquirt, aftermarket) or an SEFI ECM would make things much easier.

Keep in mind the increase needed if you have only E10 fuel in your area.

Yes, for that much boost you need an aftercooler or some good race gas along with the meth. spray.

jfg455

Thanks for the input. I was thinking that the stock ECU route was going to tax the drivers to the max with the larger injectors. I will probably just run a FAST or a Big Stuff. I am running a 12 X 24 intercooler (air to air) as well as the alcohol. I will recheck my math and see if it will be possible to run 72's with the fuel presure range that I was looking at. I have an areomotive 1000 for fuel feed and thier EFI boost referenced regulator as well. A side note; I know of some people using TPI intakes with boost running into a lean condition on #1 cyl (ie Preston) and was wondering if switching to a mini ram would cure it? Thanks again. John

junkcltr

iTrader: (1)

If you are going with a aftermarket ECM then get an SEFI. Going that route you might as well get the 83's and have room for future HP. The SEFI will handle the 83's and bigger without a problem. If you do SEFI then don't bother with the 72's.

Also, with the SEFI you can tune each cyl. so a lean condition in any hole can be fixed with injector tuning. People talk about lean cyls with the LT1 intake which is the same as a mini ram. If you use a SEFI computer you can tune down to the cyl by cyl level. At this high a HP application it would be nice. You could try the megasquirt with alternate bank firing, but at high HP you need to use batch fire and you run into not being able to do individual cyl fuel tuning.